8 BULLETIN 65(5, U. S. DEPARTMENT OF AGRICULTURE. 



Tablf 4. — Maxima, mini ma, a nil averages of data given in Table S: Chemical composition 

 of hot and cold pressed Concord grape juices. 







Sugar 







Total 





Alka- 



Alka- 







Tan- 









Total 







linity 



linity 







nin 



Juice pressed before 

 or after heating. 



Solids, 



per 

 100 cc. 



vert 

 before 

 inver- 



Non- 

 sugar 

 solids, 

 per 



acid 

 as 

 tar- 

 taric, 



acid, 

 free 

 and 



Ash, 



per 



100 cc. 



of sol- 

 uble 

 ash, 

 N/10 



of in- 

 soluble 

 ash, 

 N/10 



Free 

 tar- 

 taric 

 acid, 



Cream 



of 

 tartar, 



and 



color- 



ing 



mat- 







per 

 100 cc. 



100 cc. 



per 

 100 cc. 



bined, 



per 

 100 cc. 





acid, 



per 



100 cc. 



acid, 



per 



100 cc. 



per 

 100 cc. 



100 cc. 



ter, 



per 



100 cc. 



Maximum: 



Gms. 



Gms. 



Gms. 



Gms. 



Gms. 



Gms. 



Cc. 



Cc. 



Gms. 



Gms. 



Gms. 





17.20 

 18.50 



14.36 

 15.12 



2.84 

 3.63 



0.84 

 1.16 



0.65 

 1.04 



0.27 

 .46 



33.2 

 55.8 



3.6 



4.8 



0.24 

 .33 



062 

 1.05 



0.08 



After 



.24 



Minimum: 







15.66 

 16.44 



13.38 

 13.29 



2.25 

 3.15 



.74 

 1.01 



.55 

 .94 



.20 

 .33 



22.4 

 38.0 



2.6 

 3.8 



.09 

 .12 



.42 

 .71 



.06 



After 



.19 



Average: 







16.36 

 17.43 



13.93 

 14.03 



2.43 

 3.40 



.78 

 1.09 



.61 

 .99 



.23 

 .39 



26.9 



46.7 



3.1 

 4.2 



.16 

 .22 



.50 



.88 



.07 



After 



.21 







Average increase. 



1.07 



.10 



.97 



.31 



.38 



.16 



19.8 



1.1 



.06 



.38 



.14 



Table 4 shows very plainly that during the heating process the 

 juice acquires more body, acid constituents, and color. The increase 

 in acidity, which is very marked, is due chiefly to the presence of 

 cream of tartar and small amounts of other organic acids, principally 

 malic and tannic. The increase in nonsugar solids is due to pectin 

 substances and gums, coloring matter, and the organic acids just 

 mentioned and their salts. These various increases are due to the 

 behavior of the skin of the grape berry during the heating process. 



During the storing period the quantity of cream of tartar derived 

 through the heating process is largely eliminated through precipita- 

 tion (Tables 7 and 8), so that the stored juice contains approxi- 

 mately the same amount of this ingredient as is contained in the 

 cold-pressed juice. During the storage of the juice, part of the pec- 

 tin substances and gums and part of the tannin and coloring matter 

 are removed from the juice. With the decrease in cream of tartar 

 during storage there is a corresponding decrease in total solids, non- 

 sugar solids, total acidity, total tartaric acid, ash, and the alkalinity 

 of the water-soluble ash. 



The heating kettles are of aluminum and are steam-jacketed. 

 Steam-jacketed, glass-lined steel tanks, or wooden vats fitted with 

 aluminum steam coils, may, however, be employed with success. 

 The heating kettles, or vats, are equipped with agitators to allow 

 uniform heating of the pulp. That thorough agitation while heating 

 the crushed fruit is of the utmost importance is self-evident, since 

 to allow the mass to rest would overheat the portion next to the 

 heating surface and cause scorching. Scorching also results from 

 filling the kettles while hot. These two precautions should be closely 

 observed in order to avoid a cooked taste in the juice. 



